There is increasing use of flexible conductor cables in electrical and electronic equipment such as business machines, communication systems and computers. Concomitant with the increased use is the increased need by equipment manufacturers for cable that is color coordinated with the equipment particularly when the cable is visible to anyone viewing or using the equipment. Furthermore, it is desirable that this cable have a matte finish to eliminate glare from any exposed surface.
Conductor cables typically are comprised of a number of longitudinally extended spaced-apart conductor elements encapsulated within an insulating sheath. The conductor elements may be composed of any suitable electroconductive material that exhibits the required qualities of flexibility and strength, such as copper and the like. The insulating material is usually polyester, polyvinyl chloride or other plastic material. The insulating materials used are generally manufactured as a transparent or translucent matte film. Generally these films must be heat stabilized to control shrinkage prior to being made into cable. The cable is made by sandwiching the conductor elements between webs of adhesive coated insulating material and laminating the layers by applying heat and pressure to the sandwich. Typical methods and apparatus for making flexible cables are disclosed in U.S. Pat. Nos. 3,513,045 and 4,351,689.
Standard methods for coloring the plastic film prior to making flexible cable are unsatisfactory. Although it is possible to add pigment to the raw materials prior to extruding or forming the insulating film of material, this method is economically feasible only for very high volume production. Applying color to the surface of the film by means of dipping, spraying, or otherwise coating at least one surface of the film with a pigmented solution is also unsatisfactory. The colored coating is not sufficiently adhered to the surface or heat resistant to remain on the surfaces during the cable manufacturing process, particularly during lamination.
Applying color to the finished cable by dipping, spraying, or other coating means is also unsatisfactory. The different coefficients of expansion of the insulating material and the conductive elements cause the cable layers to separate under the conditions required for the coloring process. Furthermore, a colored coating on the surface of the cable is subject to wear by abrasion and to attack by cleaning solvents.
Flexible cable can also be colored by adding dye to the adhesive layers or by adding a layer of colored insulating material between the outer dielectric web and the conducting elements. While these methods eliminate the problems associated with surface coating, they produce true vivid colors only when used with transparent film. These methods are generally unsatisfactory for coloring translucent film because true vivid colors are unattainable due to the diffusion and refraction properties of the matte film. Furthermore, these methods increase the number of manufacturing steps required to make a finished product.
The process as disclosed herein eliminates the aforementioned problems. The desired color or colors are imparted to the insulating film by means of sublimation dyeing. This process also provides a means to impart a multicolored design and alphanumeric characters as well as solid color to the film.
The process for dyeing a continuous flexible polymeric substrate such as a film, uses a strip of transfer paper having one or more sublimable dyes deposited on one surface. The substrate and transfer paper are fed simultaneously into a heat transfer apparatus comprised of a heating means and a substrate retaining means. The layers are fed into the apparatus so that the uncoated side of the transfer paper is proximate the heating means and the substrate is proximate the substrate retaining means.
The substrate retaining means is used to hold the transfer paper securely between the substrate and the heating means. Sufficient heat is applied to the transfer paper to cause the dye to sublime from the paper and diffuse into the intertices of the substrate as it is swelled during the heating process. The color thus becomes an integral part of the substrate and is not merely a coating. The color remains stable during subsequent processing and is not affected by cleaning solvents or abrasion.
The textile industry has used sublimation dyeing of fabric for a number of years. Apparatus and methods for sublimation dyeing are disclosed in patents such as U.S. Pat. Nos. 2,911,280, 3,966,396, 4,163,642, 4,226,594 and 4,419,102. Sublimation dyeing has also been used to print graphics on keyboards and the like for membrane switches. The printing takes place just prior to final assembly of the keyboard.
It is new, however, to use sublimation dyeing to impart color into a continuous strip of flexible plastic film that is used for manufacturing flexible cable. Further, it is new to use sublimation dyeing as one of the initial steps in a cable manufacturing process. Using the method as disclosed herein also eliminates the necessity of prestabilizing film prior to making the cable. Sublimation dyeing requires a higher temperature than that normally used for stabilizing the material. Thus, the film can be stabilized and colored at the same time. Furthermore, tests show that flexible cable that has been colored by sublimation dyeing in accordance with the herein disclosed process surprisingly and unexpectedly exhibits greater resistance to being peeled apart than cable that has not been colored by this process.
The method can be further understood by referring to the following drawings .